Do indexes work with “IN” clause

Question

If I have a query like:

Select EmployeeId 
From Employee 
Where EmployeeTypeId IN (1,2,3)

and I have an index on the EmployeeTypeId

Answer 1

Usually it would, unless the IN clause covers too much of the table, and then it will do a table scan. Best way to find out in your specific case would be to run it in the query analyzer, and check out the execution plan.